1. Field of the Invention
The present invention relates to a vehicle vicinity monitoring apparatus for extracting an object from an image obtained by an imaging unit that is capable of obtaining images in a visible light range or an infrared radiation range.
2. Description of the Related Art
There has been developed a vehicle vicinity monitoring apparatus for obtaining images of one object with two imaging units mounted on a vehicle, for example, either measuring the distance up to the object based on the parallax between the obtained images, or measuring the position in an actual space of the object with respect to the vehicle, and informing the driver of whether there is an obstacle ahead of the vehicle or not (see Japanese Laid-Open Patent Publication No. 2003-216937).
According to the developed vehicle vicinity monitoring apparatus, after the object is detected in the two images obtained by the imaging units, the parallax between the obtained images with respect to the object is determined by pattern matching, and the distance up to the object is detected based on the parallax.
In order to accurately measure the position of or the distance up to the object, the angles at which the imaging units are mounted need to be determined with accuracy. Particularly, if the object exists in a distant position, then any slight difference between the mounted angles of the imaging units tends to cause a large error in the measurement of the position of or the distance up to the object. One solution is to perform an aiming process in which a target placed in a known position is imaged by the imaging units, and the mounted angles of the imaging units are determined based on the target images in the obtained images.
According to the aiming process, suitable clipping areas (image areas) are set respectively in the two images. Then, the object is extracted from the images of the clipping areas, and pattern matching and parallax detection are performed according to correlative calculations to calculate the distance up to the object. The clipping areas that are set respectively in the two images are calculated from known parameters such as the height of the imaging unit, the height of the object, etc., and can be set independently of each other.
Actually, however, the two imaging units may have slightly different heights and orientations due to a small distortion of the vehicle itself and manufacturing errors of supports of the imaging units. Therefore, the clipping areas that are independently set in the images obtained by the imaging units may not exactly match each other. According to a pattern matching process, the object image is extracted from one of the two images as a reference image, and moved the extracted image over the other image as a comparison image. If the clipping areas do not exactly match each other in the pattern matching process, then a period of time for seeking a pattern match is increased, or the object image may match another object image.
There is known a position detecting apparatus for extracting an object from an image obtained by an imaging unit mounted on a vehicle and detecting the position of the object in an actual space, while at the same time performing a correcting process for removing the effect of pitching of the vehicle (see, for example, Japanese Laid-Open Patent Publication No. 2002-5626).
There is also known a position detecting apparatus for extracting an object from an image obtained by an imaging unit mounted on a vehicle and detecting the position of the object in an actual space, while at the same time performing a correcting process for removing the effect of a lateral shift of the optical axis of the imaging unit (see, for example, Japanese Laid-Open Patent Publication No. 2002-5656).
In the known position detecting apparatus, as corrective quantities relative to a pitch angle and a pan angle with respect to the initially set optical axis of the imaging unit mounted on the vehicle increase, an image area to be processed which is set depending on an image area determined by the initially set optical axis and an object search area is liable to be shifted excessively, making it difficult to appropriately perform a process of detecting the object in a desired monitoring area around the vehicle.